This disclosure relates to maintaining print quality in xerographic developer systems. More particularly, the teachings herein are directed to apparatus and methods for operating a fuser belt assembly of a belt-nip fuser system in which a nip load profile can be sensed for use in pressure pad calibration.
Generally, the process of electrophotographic printing includes charging a photoconductive member such as a photoconductive belt or drum to a substantially uniform potential to sensitize the photoconductive surface thereof. The charged portion of the photoconductive surface is exposed to a light image from a scanning laser beam, a light emitting diode (LED) source, or other light source. This records an electrostatic latent image on the photoconductive surface. After the electrostatic latent image is recorded on the photoconductive surface, the latent image is developed in a developer system with charged toner. The toner powder image is subsequently transferred to a copy sheet and heated to permanently fuse it to the copy sheet in a fusing station.
A fusing station of a belt-nip fuser system typically includes a heated fuser roll and a fuser belt assembly formed by an endless fuser belt stretched by a plurality of rolls. Positioned within the fuser belt is a pressure pad movable between an operating position in which it is pressed against the fuser roll by the fuser belt to form a fusing nip, and a non-operating position where the pressure pad is moved away from the fuser belt.
In the operating position, the pressure pad engages an inner surface of a moving endless fuser belt and a load is placed on the pressure pad. The load on the pressure pad should be maintained at optimal settings that are balanced along the center as well as inboard and outboard edges of the pressure pad. If the load is too low or asymmetrical, image defects can occur on printed documents. Excessive loading on the pressure pad can cause excessive wear requiring frequent replacement of the pressure pads.
In various commercial products, the nip of the fuser is adjusted at the factory to within exacting tolerances, such as by placement of a pressure transducer pad placed between a fuser roll and a pressure belt. Adjustments in pressure across the length of the fuser nip is made by adjusting fuser pad preload springs to obtain a suitable pad force symmetrical distribution across the center, inboard and outboard edges. However, when the fuser belt assembly is replaced after its useful life, there is currently no procedure to accurately set the nip back to factory settings. Moreover, due to mechanical tolerances of the pressure pads, factory symmetrical settings cannot be assured upon replacement.